Sinclair is on-loan at WBA from Manchester City.
He said: "I am sure the United fans will give me stick for being at City.
"I am sure if I get to play and score, people at City would love it, but the main thing is the team gets the three points and we go there and cause an upset.
"There is never a good time to play United, it is always going to be a hard game, it doesn't matter whether they have won, lost or drawn.
"All the boys will be up for it. Playing at Old Trafford is great for any player."
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